These studies have focused on the immediate goal of defining regulatory sequences involved in the normal expression of globin genes. Plasmid vectors containing the human Alpha, Beta or Delta globin genes were constructed to study globin gene expression following introduction of these recombinant vectors into cultured mammalian cells (monkey kidney Cos cell line) by the calcium phospate precipitate technique. Function of the Delta and Beta but not Alpha globin gene promoter required enhancer sequences provided by the tandemly repeated 72 bp sequences of the SV40 viral genome. Further differences in promoter function were revealed by the 50-fold higher level of expression of the Beta globin gene compared to the Delta globin gene. Application of the expression system to the study of thalassemic Beta globin genes confirmed the utility of this sytems for quantitation of gene expression and for analyzing RNA processing defectgs. Insights into globin gene regulation gained with this approach should provide a rational basis for construction of vectors designed to faciltate DNA transfer and regulated gene transcription in mammalian cells.